Process for the production of phosphoric acid



Dec. 18, 1928.-

A. NOBLE PROCESS FOR THE PRODUCTION OF PHOSPHORIC ACID Filed Feb. 29,1924 Patented Dec. 18, 1928.-

UNITED siufres` 1,695,558 PATENT oFFicE.

ALBERT NOBLE, OF ANNISTON, ALABAMA, ASSIGNOR TO FEDERAL PHOSPHORUSCOMPANY, OF BIRMINGHAM, ALABAMA, A CORPORATION OF ALABAMA.

PROCESS FOR THE PRODUCTION OF PI-IOSPHORIC ACID.

Application filed February 29, 1924. `Serial N'o. 695,945.

This invention relates to the smelting of phosphatic material and moreparticularly, but not exclusively, t0 the manufacture of phosphoricacid; and comprises a method wherein a cliaige composed, for example, ofphosphaterock, carbon, and silica or a silicate, is heated by thecombustion of powdered coal, fuel oil, natural or producer gas, atsufficient temperature to cause the phosphorus to beI eliminated fromthe molten slag and subsequently oxidized and collecti ed, the heat fromthe oxidation of the gases being utilized tov preheat the air forconibustion and oxidation.

The object of this invention is to provide for the treatment in fuelheated furnaces of. phosphatic material and especially low gradephosphate rock whereby phosphoric acid may be economically produced, ina manner not heretofore possible;

In Order'that my invention may be fully understood, and clearlydifferentiated from the prior art, the following' description is given,whereby those skilledin the art'may practice my invention.

I proposeto combine With a hearth upon Which the charge is smelted anoverhead stack of substantially less width than the hearth, throughwhich the charge descends to the hearth and is there subjected on onesideto the action of an impinging flame or flames which smelt it,causing .its evolved gases to pass from the other side of the charge toa combustion chamber to which air is admitted by which they arecompletely oxidized, the air being preferably caused to flow down thestack through the charge. It is an important step in my invention thatthe intense heat of oxidation of the evolved gases is largely saved andeconomically utilized by its transfer to the air supplied to the furnacefor the purposes of combustion or oxidation orboth, but yespecially foroxidation as this air can he caused to flow slowly down through the dc'-sceiiding charge in the stack in such manner as to transfer its heat tothe charge in the most efficient manner and to prelieat the L latter andthus proportionately reduce the fuel required to smelt it. Obviously,the preheating of the air of combustion Will also conserve fuel andincrease the temperature of the impinging flames."

My invention lcontemplates the employ- .deep penetration'of the flames.lsinelting, therefore, results from the imping- 'ing and envelopingflame principally on one nient of a flame or flames in the heatingchamber at one side of the hearth which play over the stock pile restingon the hearth, impinging` against it and flowing freely over itsspreading base towards the combustion or oxidizing chamber at the otherSide of the hearth, causing the principal fusion zone to extend aboutthe side of the stock pile adjacent to the flame. This results insealing with the fusing stock the pile against the A surface side andthe smelting stock seals that side so that air of oxidation flowing downthrough the stack will pass out therefrom through the stock only on thesidetowards` the combustion chamber. In this Way I maintain the reducingatmosphere desirable Iin the heating chamber and supply the necessaryair in the most effective Way-to the oxidizing chamber, This gives afree flow of air through the charge in the'feedin stack and permits itsuniform escape into t e oxidizing compartment. Moreover the down. flowof air through the stock causes the dust to be filtered out of it, asthe smaller particles melt quicker than the larger pieces of stock andwill adhere to the latter and thus will not tend to become entrainedwith the air.

I have found that it is an advantage to have the preheated air enter thefurnace' along` with and in the saine direction as the 'descendingstock, as I thereby -avoid the tendency of the charge to scaffold oradhere to the side walls of the feed stack. If the evolved gases pass upthrough the feed stack, these highly heated gases, given sufficient.airv for combustion, will sinter the charge and cause it to stick to theside Walls of the stack. I have also found that by burning the evolvedgases near the surface ofthe charge on the hearth, there is animprovement in the smelting efficiency in that the heat is reflected tothe surface of the melting charge.

Ifit is desirable to do so, feldspar, shale, or other potash bearingsilicates may be used as a substitute for sand. In such cases,'thepotash is driven off and ma be collected along with the phosphoricacidfume. The silica of combustion in the silicate reacts with the lime inthe phosphate rockand isremoved from the furnace in a. manner simiy ofthe component materials.

CaaPZOsJfBsiO2e+=5C=eCasio3+2P+5Go. The mixture is based on chemicalanalysis Additional coke is added to the mixture, equivalent tol iapproximately in excess of that necesinto tlle Vfeed stack 1.

sary for the above equation, because it has been found that a certainportion is always burned away bythe air and some is carried olfentrained in the gases; hence the necessity for additional coke.

As illustrative of a typical ap aratus elnbodying the essential elementsor carrying out in the preferred manner the operation of my process,reference is made to the fol-" "lovgng drawing, in which ed stack 1,superimposed on a heating chamber 2, is shown, having burners 3 and atap hole 4. The mixture of phosphatic material, `coke and silica isintroduced through a charging door4 5iills the feed st'ack 1 and restson a hearth 6, Where theilame from burners 3 plays on it. Pren heatedair is introduced through an inlet 7, and Aafter passing downward withthe stock, combines with the evolved phosphorus and carbon monoxide atthe surface of the stock 8. The 'products of combustionV from the fuelburners and evolved gases commingle in the chamber 9 and ass out into aheat interchange 10 whic is conventionally illustrated. Air is drawnthrough ports 11, and after passing through the heat interchange, isforced by a fan 12 After the heat has been -absorbed from the phosphoricacid bearing gases, they are drawn away by a fan 13 and forced into theheader of an electrical precipitator 14 which comprises pipes 15, in-

sulated wires 16, a source of current 17, a

round connection 18, and an acid receiving asin 19.`

. I prefer conducting my process in this apparatus in the followingmanner A normal charging mixture may consist of 1500 lbs.phosphatefrock, analyzing 15% 1 phosporus, 350 lbs. sand and 357 lbs.coke,

includingthe excess required to make up losses. There will be variationsfrom these I proportions, depending on the analysis of the componentmaterials. This mixture is introduced through the charging door 5 untilthe` charge il s up that portion of the 'feed' stack connecting with theheating.

have been in operation a short time, the heat begins to decompose thepliosphatic material, principally on the burner side of the stock pile 8when phosphorus fume and carbon monoxide will be evolved. These ga'sesare burned principally at the surface of.the other side of the stockpile 8 and supply heat through the interchanger to raise the temperatureof the combustion of the evolved gases. When the gases are being evolvedat a uniform rate the feed stack is filled to air inlet 7. As the slagcollects on the hearth it is kept iri a molten condition by the flameiml'iinging on and cnveloping or encircling the stock on the hearth 6,so that periodically this slag may be tapped as is practiced in anslagging furnace operation. The phosphoric acid produced may becollected in the electrical precipitator as shown, or in any`satisfactory collecting equipment as an absorption tower or condenser.

Though I have described with great particularity the details of theembodiment of the invention herein shown, it is not to be construed thatI am limited thereto, as

changes in arrangement and substitution of equivalents may be made bythose skilled inthe art Without departing from the invention as definedin the appended claims.

I do not claim herein the apparatus, as this application, because ofdivisionalrequirements, is limited to the process hereinbeforedescribed.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent, is

1. A process for the manufacture of phosphoric acid, which consists incharging a mixture of phos hate rock, silica and carbon into a fee stackdisposed over the hearth of a heating chamber, impinging a flame on thecharge in the heating chamber, passing air downwardly through the feedstack, oxidizing the evolved gases during their sojourn in the heatingchamber, transferring heat from the gases to for combustion of the fuel,an collecting the oxidized phos horus compounds.

2. A process or the manufacture of phosphoric acid, which consists incharging a mixture of hosphate rock, silica and carbon into a. eed stackdisposed over the hearth of a heating chamber, impingingea flame on thecharge inthe heatin cham passing air downwardly throng the feed stack,oxidizing the evolved gases during their sojourn in the heating chamber,transferring heat from the gases to reheat air for combutsion of thefuel and or the oxidization of the gases, and collecting the oxidizedphosphorus compounds.

3. A process forA the'manufacture of phosphoric acid, whichA consists incharging a mixture of phosphate rock, silica and carreheat air memes honinto a feed stach dispesed over the hearth of a heating chamber,impinging a lame on one side only of the charge in the heating chamber,passing air downwardly through the feed stack, oxidizing the evolvedgases ,during their sojourn in'the heating chamber, transferring heatfrom the gases to preheat air for combustion of the fuel, and collectingthe oxidized phosphorus compounds.

4. A process for the manufacture of phosphoric acid, whicl1 consists incharging a mixture of phosphate'rock, silica and carbon through a feedstack onto a hearth, irnpinging a flame on the surface of thecharge onthehearth, passing preheated air down- 5. A process for the manufactureof phos-` phoric acid, which consists in charging a mixture of phosphaterock, silica and carhonthrough a feed stack onto a hearth, impingingv aflame on one side of the surface of the charge resting on the hearth,admitting air to the gases on the other side of the charge foroxidation, and collectingthe oxidized phosphorus compounds.

In tcstimf'my Whereof alhx my signature.

' ALBERT NBLE.

